Many methods are known in industry for the manufacture of silver halide emulsions. Disclosures concerning methods of production are found in Chemie et Physique Photographique by P. Glafkides, Paul Montel Co., 1967; Photographic Emulsion Chemistry by G. F. Duffin, Focal Press Co., 1966; and in Making and Coating Photographic Emulsions by V. L. Zelikman, Focal Press Co., 1964, etc. Silver halides include silver bromide, silver iodide, silver chloride, and mixed crystals of silver iodobromide and silver chlorobromide etc. The acid method, neutral method, ammonia method etc. are various methods used for the production of silver halide emulsion. The single jet method, double jet method and a combination thereof are used as methods for reacting soluble silver salts and soluble halogen salts. Furthermore, the controlled double jet method maintains the silver ion concentration constant during the formation of the silver halide crystals.
Generally, the acid method is most often used in the production of lower speed, silver halide crystal grains having relatively fine grains. Conversely, the ammonia method is most often used in the production of higher speed silver halide crystal grains having relatively large grains. With ammonia method, the solubility of the silver halide is increased as a result of the formation of silver ions and complex ions. Thus, it is easy to grow large grains using the ammonia method.
The acid method is often used for production of silver chloride and silver chlorobromide emulsions while the ammonia method is frequently used for production of high speed silver iodobromide emulsions.
The acid method is preferably used in the production of silver chloride or silver chlorobromide emulsions in photographic materials where large grains are not required for high speed performance. Alternatively, it may be sufficiently possible to realize larger grain sizes without using a silver halide solvent such as ammonia due to the high acid solubility of silver chloride or chlorobromide as compared to silver iodobromide. Furthermore, the pH of the system increases unavoidably when ammonia is used in the production process. Compared with silver iodobromide, silver chloride and silver chlorobromide are susceptible to fog when processed under alkaline conditions.
On the other hand, silver chloride and silver chlorobromide emulsions are widely used in photographic prints, noteably color prints. Photographic stability, from production of the photosensitive materials until their use under various prevailing conditions is important to allow rapid processing of these materials.
Specific characteristics related to handling include reliability under various exposure conditions; namely exposure luminance and exposure temperature etc., latent image shelf-life under storage conditions from exposure until processing, reliability under various processing conditions, and pressure resistance during these processes.
Hitherto, photographic materials have made some remarkable advances in these respects but have not yet reached a satisfactory level. In particular, with the recent development of mini laboratories, different processing conditions are employed as compared to those in conventional large-scale developing laboratories. The emphasis on the performance demands of the photosensitive materials is also changing accordingly.